This invention relates to a drum-type magnetic separator of horizontal arrangement to handle mixed granular feeds in which the feed material is deposited on the drum shell and moves through a magnetic field of stationary magnets. The nonmagnetic particles are separated during movement through the magnetic field and the magnetic material falls away from the collecting surface after passage through the magnetic field.
Prior art stationary-magnet drum separators have a cylindrical drum member within which a magnet bank is fixed. During rotation of the drum shell about the magnet bank the separated metallic particles are moved into a discharge hopper with the aid of scraping flights. A feeder is arranged ahead of the drum inlet and batches the material by volumetric control, distributing it in a uniform layer over the width of the collecting surface of the drum. When the drum rotates, the nonmagnetic particles within the layer of material slide off the collecting surface into a chute and the magnetic constituents likewise slip off the collecting surface of the drum shell when they have passed through the magnetic field and drop into a suitably designed discharge hopper.
The main disadvantage of such separating apparatus is that the entire feed material to be treated has to be distributed over the peripheral collecting surface of the drum and pass through the magnetic field, which reduces the throughput rate, especially in the case of feeds having a high content of nonmagnetic material, such as sand. As both the feeder and discharge device must be outside the drum, the former above and the latter below the collecting surface, the overall height of the apparatus is fairly considerable and only a short drop remains from the drum shell for the separated particles. A further drawback is that the centrifugal force generated as the rotational speed of the drum is increased counters the effect of magnetic adhesion, so that frequently magnetic particles fall away and are lost. This discharge by acquired momentum is intensified by the radial acceleration induced by the scraping flights. Further, variation in the bulk density of the feed causes the driving torque of the drum to fluctuate, thereby giving rise to stalling of the motor or belt slippage.